Did not answer, no message left

When I answered, they hung up without saying anything.

Incoming call from this phone number while I was on another call. When I try dialing back, there is silence, no ring, no answer. Reverse look-up reveals a location of Los Angeles, CA 90013-1217, with "CommPartners - CA" and no identifying listing name.

Tried to call back said Server was busy.

Missed a call from this number, called it back and no answer either. Not even a ring tone sound, very strange. This is the first time I've received a call from this number.